There are at least 400 enzymes identified as protein kinases. These enzymes catalyze the phosphorylation of target protein substrates. The phosphorylation is usually a transfer reaction of a phosphate group from ATP to the protein substrate. The specific structure in the target substrate to which the phosphate is transferred is a tyrosine, serine or threonine residue. Since these amino acid residues are the target structures for the phosphoryl transfer, these protein kinase enzymes are commonly referred to as tyrosine kinases or serine/threonine kinases.
The phosphorylation reactions, and counteracting phosphatase reactions, at the tyrosine, serine and threonine residues are involved in countless cellular processes that underlie responses to diverse intracellular signals (typically mediated through cellular receptors), regulation of cellular functions, and activation or deactivation of cellular processes. A cascade of protein kinases often participate in intracellular signal transduction and are necessary for the realization of these cellular processes. Because of their ubiquity in these processes, the protein kinases can be found as an integral part of the plasma membrane or as cytoplasmic enzymes or localized in the nucleus, often as components of enzyme complexes. In many instances, these protein kinases are an essential element of enzyme and structural protein complexes that determine where and when a cellular process occurs within a cell.
Protein Tyrosine Kinases. Protein tyrosine kinases (PTKs) are enzymes which catalyse the phosphorylation of specific tyrosine residues in cellular proteins. This post-translational modification of these substrate proteins, often enzymes themselves, acts as a molecular switch regulating cell proliferation, activation or differentiation (for review, see Schlessinger and Ulrich, 1992, Neuron 9:383-391). Aberrant or excessive PTK activity has been observed in many disease states including benign and malignant proliferative disorders as well as diseases resulting from inappropriate activation of the immune system (e.g., autoimmune disorders), allograft rejection, and graft vs. host disease. In addition, endothelial-cell specific receptor PTKs such as KDR and Tie-2 mediate the angiogenic process, and are thus involved in supporting the progression of cancers and other diseases involving inappropriate vascularization (e.g., diabetic retinopathy, choroidal neovascularization due to age-related macular degeneration, psoriasis, arthritis, retinopathy of prematurity, infantile hemangiomas).
Tyrosine kinases can be of the receptor-type (having extracellular, transmembrane and intracellular domains) or the non-receptor type (being wholly intracellular).
Receptor Tyrosine Kinases (RTKs). The RTKs comprise a large family of transmembrane receptors with diverse biological activities. At present, at least nineteen (19) distinct RTK subfamilies have been identified. The receptor tyrosine kinase (RTK) family includes receptors that are crucial for the growth and differentiation of a variety of cell types (Yarden and Ullrich, Ann. Rev. Biochem. 57:433-478, 1988; Ullrich and Schlessinger, Cell 61:243-254, 1990). The intrinsic function of RTKs is activated upon ligand binding, which results in phosphorylation of the receptor and multiple cellular substrates, and subsequently in a variety of cellular responses (Ullrich & Schlessinger, 1990, Cell 61:203-212). Thus, receptor tyrosine kinase mediated signal transduction is initiated by extracellular interaction with a specific growth factor (ligand), typically followed by receptor dimerization, stimulation of the intrinsic protein tyrosine kinase activity and receptor trans-phosphorylation. Binding sites are thereby created for intracellular signal transduction molecules and lead to the formation of complexes with a spectrum of cytoplasmic signaling molecules that facilitate the appropriate cellular response. (e.g., cell division, differentiation, metabolic effects, changes in the extracellular microenvironment) see Schlessinger and Ullrich, 1992, Neuron 9:1-20.
Proteins with SH2 (src homology-2) or phosphotyrosine binding (PTB) domains bind activated tyrosine kinase receptors and their substrates with high affinity to propagate signals into cell. Both of the domains recognize phosphotyrosine. (Fantl et al., 1992, Cell 69:413-423; Songyang et al., 1994, Mol. Cell. Biol. 14:2777-2785; Songyang et al., 1993, Cell 72:767-778; and Koch et al., 1991, Science 252:668-678; Shoelson, Curr. Opin. Chem. Biol. (1997), 1(2), 227-234; Cowburn, Curr. Opin. Struct. Biol. (1997), 7(6), 835-838). Several intracellular substrate proteins that associate with receptor tyrosine kinases (RTKs) have been identified. They may be divided into two principal groups: (1) substrates which have a catalytic domain; and (2) substrates which lack such a domain but serve as adapters and associate with catalytically active molecules (Songyang et al., 1993, Cell 72:767-778). The specificity of the interactions between receptors or proteins and SH2 or PTB domains of their substrates is determined by the amino acid residues immediately surrounding the phosphorylated tyrosine residue. For example, differences in the binding affinities between SH2 domains and the amino acid sequences surrounding the phosphotyrosine residues on particular receptors correlate with the observed differences in their substrate phosphorylation profiles (Songyang et al., 1993, Cell 72:767-778). Observations suggest that the function of each receptor tyrosine kinase is determined not only by its pattern of expression and ligand availability but also by the array of downstream signal transduction pathways that are activated by a particular receptor as well as the timing and duration of those stimuli. Thus, phosphorylation provides an important regulatory step which determines the selectivity of signaling pathways recruited by specific growth factor receptors, as well as differentiation factor receptors.
Several receptor tyrosine kinases such as FGFR-1, PDGFR, TIE-2 and c-Met, and growth factors that bind thereto, have been suggested to play a role in angiogenesis, although some may promote angiogenesis indirectly (Mustonen and Alitalo, J. Cell Biol. 129:895-898, 1995). One such receptor tyrosine kinase, known as □fetal liver kinase 1□ (FLK-1), is a member of the type III subclass of RTKs. An alternative designation for human FLK-1 is “kinase insert domain-containing receptor” (KDR) (Terman et al., Oncogene 6:1677-83, 1991). Another alternative designation for FLK-1/KDR is “vascular endothelial cell growth factor receptor 2” (VEGFR-2) since it binds VEGF with high affinity. The murine version of FLK-1/VEGFR-2 has also been called NYK (Oelrichs et al, Oncogene 8(1):11-15, 1993). DNAs encoding mouse, rat and human FLK-1 have been isolated, and the nucleotide and encoded amino acid sequences reported (Matthews et al., Proc. Natl. Acad. Sci. USA, 88:9026-30, 1991; Terman et al., 1991, supra; Terman et al., Biochem. Biophys. Res. Comm. 187:1579-86, 1992; Sarzani et al., supra; and Millauer et al., Cell 72:835-846, 1993). Numerous studies such as those reported in Millauer et al., supra, suggest that VEGF and FLK-1/KDR/VEGFR-2 are a ligand-receptor pair that play an important role in the proliferation of vascular endothelial cells, and formation and sprouting of blood vessels, termed vasculogenesis and angiogenesis, respectively.
Another type III subclass RTK designated “fms-like tyrosine kinase-1” (Flt-1) is related to FLK-1/KDR (DeVries et al. Science 255;989-991, 1992; Shibuya et al., Oncogene 5:519-524, 1990). An alternative designation for Flt-1 is “vascular endothelial cell growth factor receptor 1” (VEGFR-1). To date, members of the FLK-1/KDR/VEGFR-2 and Flt-1/VEGFR-1 subfamilies have been found expressed primarily on endothelial cells. These subclass members are specifically stimulated by members of the vascular endothelial cell growth factor (VEGF) family of ligands (Klagsburn and D'Amore, Cytokine & Growth Factor Reviews 7: 259-270, 1996). Vascular endothelial cell growth factor (VEGF) binds to Flt-1 with higher affinity than to FLK-1/KDR and is mitogenic toward vascular endothelial cells (Terman et al., 1992, supra; Mustonen et al. supra; DeVries et al., supra). Flt-1 is believed to be essential for endothelial organization during vascular development. Flt-1 expression is associated with early vascular development in mouse embryos, and with neovascularization during wound healing (Mustonen and Alitalo, supra). Expression of Flt-1 in monocytes, osteoclasts, and osteoblasts, as well as in adult tissues such as kidney glomeruli suggests an additional function for this receptor that is not related to cell growth (Mustonen and Alitalo, supra).
As previously stated, recent evidence suggests that VEGF plays a role in the stimulation of both normal and pathological angiogenesis (Jakeman et al., Endocrinology 133: 848-859, 1993; Kolch et al., Breast Cancer Research and Treatment 36: 139-155, 1995; Ferrara et al., Endocrine Reviews 18(1); 4-25, 1997; Ferrara et al., Regulation of Angiogenesis (ed. L. D. Goldberg and E. M. Rosen), 209-232, 1997). In addition, VEGF has been implicated in the control and enhancement of vascular permeability (Connolly, et al., J. Biol. Chem. 264: 20017-20024, 1989; Brown et al., Regulation of Angiogenesis (ed. L. D. Goldberg and E. M. Rosen), 233-269, 1997). Different forms of VEGF arising from alternative splicing of mRNA have been reported, including the four species described by Ferrara et al. (J. Cell. Biochem. 47:211-218, 1991). Both secreted and predominantly cell-associated species of VEGF have been identified by Ferrara et al. supra, and the protein is known to exist in the form of disulfide linked dimers.
Several related homologs of VEGF have recently been identified. However, their roles in normal physiological and disease processes have not yet been elucidated. In addition, the members of the VEGF family are often coexpressed with VEGF in a number of tissues and are, in general, capable of forming heterodimers with VEGF. This property likely alters the receptor specificity and biological effects of the heterodimers and further complicates the elucidation of their specific functions as illustrated below (Korpelainen and Alitalo, Curr. Opin. Cell Biol., 159-164, 1998 and references cited therein).
Placenta growth factor (PlGF) has an amino acid sequence that exhibits significant homology to the VEGF sequence (Park et al., J. Biol. Chem. 269:25646-54, 1994; Maglione et al. Oncogene 8:925-31, 1993). As with VEGF, different species of PlGF arise from alternative splicing of mRNA, and the protein exists in dimeric form (Park et al., supra). PlGF-1 and PlGF-2 bind to Flt-1 with high affinity, and PlGF-2 also avidly binds to neuropilin-1 (Migdal et al, J. Biol. Chem. 273 (35): 22272-22278), but neither binds to FLK-1/KDR (Park et al., supra). PlGF has been reported to potentiate both the vascular permeability and mitogenic effect of VEGF on endothelial cells when VEGF is present at low concentrations (purportedly due to heterodimer formation) (Park et al., supra).
VEGF-B is produced as two isoforms (167 and 185 residues) that also appear to bind Flt-1/VEGFR-1. It may play a role in the regulation of extracellular matrix degradation, cell adhesion, and migration through modulation of the expression and activity of urokinase type plasminogen activator and plasminogen activator inhibitor 1 (Pepper et al, Proc. Natl. Acad. Sci. U.S.A. (1998), 95(20): 11709-11714).
VEGF-C was originally cloned as a ligand for VEGFR-3/Flt-4 which is primarily expressed by lymphatic endothelial cells. In its fully processed form, VEGF-C can also bind KDR/VEGFR-2 and stimulate proliferation and migration of endothelial cells in vitro and angiogenesis in in vivo models (Lymboussaki et al, Am. J. Pathol. (1998), 153(2): 395-403; Witzenbichler et al, Am. J. Pathol. (1998), 153(2), 381-394). The transgenic overexpression of VEGF-C causes proliferation and enlargement of only lymphatic vessels, while blood vessels are unaffected. Unlike VEGF, the expression of VEGF-C is not induced by hypoxia (Ristimaki et al, J. Biol. Chem. (1998), 273(14),8413-8418).
The most recently discovered VEGF-D is structurally very similar to VEGF-C. VEGF-D is reported to bind and activate at least two VEGFRs, VEGFR-3/Flt-4 and KDR/VEGFR-2. It was originally cloned as a c-fos inducible mitogen for fibroblasts and is most prominently expressed in the mesenchymal cells of the lung and skin (Achen et al, Proc. Natl. Acad. Sci. U.S.A. (1998), 95(2), 548-553 and references therein).
As for VEGF, VEGF-C and VEGF-D have been claimed to induce increases in vascular permeability in vivo in a Miles assay when injected into cutaneous tissue (PCT/US97/14696; WO98/07832, Witzenbichler et al., supra). The physiological role and significance of these ligands in modulating vascular hyperpermeability and endothelial responses in tissues where they are expressed remains uncertain.
There has been recently reported a virally encoded, novel type of vascular endothelial growth factor, VEGF-E (NZ-7 VEGF), which preferentially utilizes KDR/Flk-1 receptor and carries a potent mitotic activity without heparin-binding domain (Meyer et al, EMBO J. (1999), 18(2), 363-374; Ogawa et al, J. Biol. Chem. (1998), 273(47), 31273-31282.). VEGF-E sequences possess 25% homology to mammalian VEGF and are encoded by the parapoxyirus Orf virus (OV). This parapoxyirus that affects sheep and goats and occasionally, humans, to generate lesions with angiogenesis. VEGF-E is a dimer of about 20 kDa with no basic domain nor affinity for heparin, but has the characteristic cysteine knot motif present in all mammalian VEGFs, and was surprisingly found to possess potency and bioactivities similar to the heparin-binding VEGF165 isoform of VEGF-A, i.e. both factors stimulate the release of tissue factor (TF), the proliferation, chemotaxis and sprouting of cultured vascular endothelial cells in vitro and angiogenesis in vivo. Like VEGF165, VEGF-E was found to bind with high affinity to VEGF receptor-2 (KDR) resulting in receptor autophosphorylation and a biphasic rise in free intracellular Ca2+ concentrations, while in contrast to VEGF165, VEGF-E did not bind to VEGF receptor-1 (Flt-1).
Based upon emerging discoveries of other homologs of VEGF and VEGFRs and the precedents for ligand and receptor heterodimerization, the actions of such VEGF homologs may involve formation of VEGF ligand heterodimers, and/or heterodimerization of receptors, or binding to a yet undiscovered VEGFR (Witzenbichler et al., supra). Also, recent reports suggest neuropilin-1 (Migdal et al, supra) or VEGFR-3/Flt-4 (Witzenbichler et al., supra), or receptors other than KDR/VEGFR-2 may be involved in the induction of vascular permeability (Stacker, S. A., Vitali, A., Domagala, T., Nice, E., and Wilks, A. F., “Angiogenesis and Cancer” Conference, Amer. Assoc. Cancer Res., January 1998, Orlando, Fla.; Williams, Diabetelogia 40: S118-120 (1997)).
Tie-2 (TEK) is a member of a recently discovered family of endothelial cell specific receptor tyrosine kinases which is involved in critical angiogenic processes, such as vessel branching, sprouting, remodeling, maturation and stability. Tie-2 is the first mammalian receptor tyrosine kinase for which both agonist ligand(s) (e.g., Angiopoietin1 (“Ang1”), which stimulates receptor autophosphorylation and signal transduction), and antagonist ligand(s) (e.g., Angiopoietin2 (“Ang2”)), have been identified. Knock-out and transgenic manipulation of the expression of Tie-2 and its ligands indicates tight spatial and temporal control of Tie-2 signaling is essential for the proper development of new vasculature. The current model suggests that stimulation of Tie-2 kinase by the Ang1 ligand is directly involved in the branching, sprouting and outgrowth of new vessels, and recruitment and interaction of periendothelial support cells important in maintaining vessel integrity and inducing quiescence. The absence of Ang1 stimulation of Tie-2 or the inhibition of Tie-2 autophosphorylation by Ang2, which is produced at high levels at sites of vascular regression, may cause a loss in vascular structure and matrix contacts resulting in endothelial cell death, especially in the absence of growth/survival stimuli. The situation is however more complex, since at least two additional Tie-2 ligands (Ang3 and Ang4) have recently been reported, and the capacity for heterooligomerization of the various agonistic and antagonistic angiopoietins, thereby modifying their activity, has been demonstrated. Targeting Tie-2 ligand-receptor interactions as an antiangiogenic therapeutic approach is thus less favored and a kinase inhibitory strategy preferred.
The soluble extracellular domain of Tie-2 (“ExTek”) can act to disrupt the establishment of tumor vasculature in a breast tumor xenograft and lung metastasis models and in tumor-cell mediated ocular neovasculatization. By adenoviral infection, the in vivo production of mg/ml levels ExTek in rodents may be achieved for 7-10 days with no adverse side effects. These results suggest that disruption of Tie-2 signaling pathways in normal healthy animals may be well tolerated. These Tie-2 inhibitory responses to ExTek may be a consequence sequestration of ligand(s) and/or generation of a nonproductive heterodimer with full-length Tie-2.
Recently, significant upregulation of Tie-2 expression has been found within the vascular synovial pannus of arthritic joints of humans, consistent with a role in the inappropriate neovascularization. This finding suggests that Tie-2 plays a role in the progression of rheumatoid arthritis. Point mutations producing constitutively activated forms of Tie-2 have been identified in association with human venous malformation disorders. Tie-2 inhibitors are, thereful, useful in treating such disorders, and in other situations of inappropriate neovascularization.
The Non-Receptor Tyrosine Kinases. The non-receptor tyrosine kinases represent a collection of cellular enzymes which lack extracellular and transmembrane sequences. At present, over twenty-four individual non-receptor tyrosine kinases, comprising eleven (11) subfamilies (Src, Frk, Btk, Csk, Abl, Zap70, Fes/Fps, Fak, Jak, Ack and LIMK) have been identified. At present, the Src subfamily of non-receptor tyrosine kinases is comprised of the largest number of PTKs and include Src, Yes, Fyn, Lyn, Lck, Blk, Hck, Fgr and Yrk. The Src subfamily of enzymes has been linked to oncogenesis and immune responses. A more detailed discussion of non-receptor tyrosine kinases is provided in Bohlen, 1993, Oncogene 8:2025-2031, which is incorporated herein by reference.
Many of the tyrosine kinases, whether an RTK or non-receptor tyrosine kinase, have been found to be involved in cellular signaling pathways involved in numerous pathogenic conditions, including cancer, psoriasis, and other hyperproliferative disorders or hyper-immune responses.
Development of Compounds to Modulate the PTKs. In view of the surmised importance of PTKs to the control, regulation, and modulation of cell proliferation, the diseases and disorders associated with abnormal cell proliferation, many attempts have been made to identify receptor and non-receptor tyrosine kinase “inhibitors” using a variety of approaches, including the use of mutant ligands (U.S. Pat. No. 4,966,849), soluble receptors and antibodies (Application No. WO 94/10202; Kendall & Thomas, 1994, Proc. Natl. Acad. Sci 90:10705-09; Kim et al., 1993, Nature 362:841-844), RNA ligands (Jellinek, et al., Biochemistry 33:10450-56; Takano, et al., 1993, Mol. Bio. Cell 4:358A; Kinsella, et al. 1992, Exp. Cell Res. 199:56-62; Wright, et al., 1992, J. Cellular Phys. 152:448-57) and tyrosine kinase inhibitors (WO 94/03427; WO 92/21660; WO 91/15495; WO 94/14808; U.S. Pat. No. 5,330,992; Mariani, et al., 1994, Proc. Am. Assoc. Cancer Res. 35:2268).
More recently, attempts have been made to identify small molecules which act as tyrosine kinase inhibitors. For example, bis monocyclic, bicyclic or heterocyclic aryl compounds (PCT WO 92/20642) and vinylene-azaindole derivatives (PCT WO 94/14808) have been described generally as tyrosine kinase inhibitors. Styryl compounds (U.S. Pat. No. 5,217,999), styryl-substituted pyridyl compounds (U.S. Pat. No. 5,302,606), certain quinazoline derivatives (EP Application No. 0 566 266 A1; Expert Opin. Ther. Pat. (1998), 8(4): 475-478), selenoindoles and selenides (PCT WO 94/03427), tricyclic polyhydroxylic compounds (PCT WO 92/21660) and benzylphosphonic acid compounds (PCT WO 91/15495) have been described as compounds for use as tyrosine kinase inhibitors for use in the treatment of cancer. Anilinocinnolines (PCT WO97/34876) and quinazoline derivative compounds (PCT WO97/22596; PCT WO97/42187) have been described as inhibitors of angiogenesis and vascular permeability.
In addition, attempts have been made to identify small molecules which act as serine/threonine kinase inhibitors. For example, bis(indolylmaleimide) compounds have been described as inhibiting particular PKC serine/threonine kinase isoforms whose signal transducing function is associated with altered vascular permeability in VEGF-related diseases (PCT WO97/40830; PCT WO97/40831).
Plk-1 Kinase Inhibitors
Plk-1 is a serine/threonine kinase which is an important regulator of cell cycle progression. It plays critical roles in the assembly and the dynamic function of the mitotic spindle apparatus. Plk-1 and related kinases have also been shown to be closely involved in the activation and inactivation of other cell cycle regulators, such as cyclin-dependent kinases. High levels of Plk-1 expression are associated with cell proliferation activities. It is often found in malignant tumors of various origins. Inhibitors of Plk-1 are expected to block cancer cell proliferation by disrupting processes involving mitotic spindles and inappropriately activated cyclin-dependent kinases.
Cdc2/Cyclin B Kinase Inhibitors (Cdc2 is also known as cdk1)
Cdc2/cyclin B is another serine/threonine kinase enzyme which belongs to the cyclin-dependent kinase (cdks) family. These enzymes are involved in the critical transition between various phases of cell cycle progression. It is believed that uncontrolled cell proliferation, which is the hallmark of cancer is dependent upon elevated cdk activities in these cells. The inhibition of elevated cdk activities in cancer cells by cdc2/cyclin B kinase inhibitors could suppress proliferation and may restore the normal control of cell cycle progression.
The regulation of CDK activation is complex, but requires the association of the CDK with a member of the cyclin family of regulatory subunits (Draetta, Trends in Cell Biology, 3:287-289 (1993)); Murray and Kirschner, Nature, 339:275-280 (1989); Solomon et al., Molecular Biology of the Cell, 3:13-27 (1992)). A further level of regulation occurs through both activating and inactivating phosphorylations of the CDK subunit (Draetta, Trends in Cell Biology, 3:287-289 (1993)); Murray and Kirschner, Nature, 339:275-280 (1989); Solomon et al., Molecular Biology of the Cell, 3:13-27 (1992); Ducommun et al., EMBO Journal, 10:3311-3319 (1991); Gautier et al., Nature 339:626-629 (1989); Gould and Nurse, Nature, 342:39-45 (1989); Krek and Nigg, EMBO Journal, 10:3331-3341 (1991); Solomon et al., Cell, 63:1013-1024 (1990)). The coordinate activation and inactivation of different cyclin/CDK complexes is necessary for normal progression through the cell cycle (Pines, Trends in Biochemical Sciences, 18:195-197 (1993); Sherr, Cell, 73:1059-1065 (1993)). Both the critical G1-S and G2-M transitions are controlled by the activation of different cyclin/CDK activities. In G1, both cyclin D/CDK4 and cyclin E/CDK2 are thought to mediate the onset of S-phase (Matsushima et al., Molecular & Cellular Biology, 14:2066-2076 (1994); Ohtsubo and Roberts, Science, 259:1908-1912 (1993); Quelle et al., Genes & Development, 7:1559-1571 (1993); Resnitzky et al., Molecular & Cellular Biology, 14:1669-1679 (1994)). Progression through S-phase requires the activity of cyclin A/CDK2 (Girard et al., Cell, 67:1169-1179 (1991); Pagano et al., EMBO Journal, 11:961-971 (1992); Rosenblatt et al., Proceedings of the National Academy of Science USA, 89:2824-2828 (1992); Walker and Maller, Nature, 354:314-317 (1991); Zindy et al., Biochemical & Biophysical Research Communications, 182:1144-1154 (1992)) whereas the activation of cyclin A/cdc2 (CDK1) and cyclin B/cdc2 are required for the onset of metaphase (Draetta, Trends in Cell Biology, 3:287-289 (1993)); Murray and Kirschner, Nature, 339:275-280 (1989); Solomon et al., Molecular Biology of the Cell, 3:13-27 (1992); Girard et al., Cell, 67:1169-1179 (1991); Pagano et al., EMBO Journal, 11:961-971 (1992); Rosenblatt et al., Proceedings of the National Academy of Science USA, 89:2824-2828 (1992); Walker and Maller, Nature, 354:314-317 (1991); Zindy et al., Biochemical & Biophysical Research Communications, 182:1144-1154 (1992)). It is not surprising, therefore, that the loss of control of CDK regulation is a frequent event in hyperproliferative diseases and cancer. (Pines, Current Opinion in Cell Biology, 4:144-148 (1992); Lees, Current Opinion in Cell Biology, 7:773-780 (1995); Hunter and Pines, Cell, 79:573-582 (1994)).
Inhibitors of kinases involved in mediating or maintaining disease states represent novel therapies for these disorders. Examples of such kinases include, but are not limited to: (1) inhibition of c-Src (Brickell, Critical Reviews in Oncogenesis, 3:401-406 (1992); Courtneidge, Seminars in Cancer Biology, 5:236-246 (1994), raf (Powis, Pharmacology & Therapeutics, 62:57-95 (1994)) and the cyclin-dependent kinases (CDKs) 1, 2 and 4 in cancer (Pines, Current Opinion in Cell Biology, 4:144-148 (1992); Lees, Current Opinion in Cell Biology, 7:773-780 (1995); Hunter and Pines, Cell, 79:573-582 (1994)), (2) inhibition of CDK2 or PDGF-R kinase in restenosis (Buchdunger et al., Proceedings of the National Academy of Science USA, 92:2258-2262 (1995)), (3) inhibition of CDK5 and GSK3 kinases in Alzheimers (Hosoi et al., Journal of Biochemistry (Tokyo), 117:741-749 (1995); Aplin et al., Journal of Neurochemistry, 67:699-707 (1996), (4) inhibition of c-Src kinase in osteoporosis (Tanaka et al., Nature, 383:528-531 (1996), (5) inhibition of GSK-3 kinase in type-2 diabetes (Borthwick et al., Biochemical & Biophysical Research Communications, 210:738-745 (1995), (6) inhibition of the p38 kinase in inflammation (Badger et al., The Journal of Pharmacology and Experimental Therapeutics, 279:1453-1461 (1996)), (7) inhibition of VEGF-R 1-3 and TIE-1 and -2 kinases in diseases which involve angiogenesis (Shawver et al., Drug Discovery Today, 2:50-63 (1997)), (8) inhibition of UL97 kinase in viral infections (He et al., Journal of Virology, 71:405-411 (1997)), (9) inhibition of CSF-1R kinase in bone and hematopoetic diseases (Myers et al., Bioorganic & Medicinal Chemistry Letters, 7:421-424 (1997), and (10) inhibition of Lck kinase in autoimmune diseases and transplant rejection (Myers et al., Bioorganic & Medicinal Chemistry Letters, 7:417-420 (1997).
It is additionally possible that inhibitors of certain kinases may have utility in the treatment of diseases when the kinase is not misregulated, but it nonetheless essential for maintenance of the disease state. In this case, inhibition of the kinase activity would act either as a cure or palliative for these diseases. For example, many viruses, such as human papilloma virus, disrupt the cell cycle and drive cells into the S-phase of the cell cycle (Vousden, FASEB Journal, 7:8720879 (1993)). Preventing cells from entering DNA synthesis after viral infection by inhibition of essential S-phase initiating activities such as CDK2, may disrupt the virus life cycle by preventing virus replication. This same principle may be used to protect normal cells of the body from toxicity of cycle-specific chemotherapeutic agents (Stone et al., Cancer Research, 56:3199-3202 (1996); Kohn et al., Journal of Cellular Biochemistry, 54:44-452 (1994)). Inhibition of CDKs 2 or 4 will prevent progression into the cycle in normal cells and limit the toxicity of cytotoxics which act in S-phase, G2 or mitosis. Furthermore, CDK2/cyclin E activity has also been shown to regulate NF-kB. Inhibition of CDK2 activity stimulates NF-kB-dependent gene expression, an event mediated through interactions with the p300 coactivator (Perkins et al., Science, 275:523-527 (1997)). NF-kB regulates genes involved in inflammatory responses (such as hematopoetic growth factors, chemokines and leukocyte adhesion molecules) (Baeuerle and Henkel, Annual Review of Immunology, 12:141-179 (1994)) and may be involved in the suppression of apoptotic signals within the cell (Beg and Baltimore, Science, 274:782-784 (1996); Wang et al., Science, 274:784-787 (1996); Van Antwerp et al., Science, 274:787-789 (1996)). Thus, inhibition of CDK2 may suppress apoptosis induced by cytotoxic drugs via a mechanism which involves NF-kB. This therefore suggests that inhibition of CDK2 activity may also have utility in other cases where regulation of NF-KB plays a role in etiology of disease. A further example may be take from fungal infections: Aspergillosis is a common infection in immune-compromised patients (Armstrong, Clinical Infectious Diseases, 16:1-7 (1993)). Inhibition of the Aspergillus kinases Cdc2/CDC28 or Nim A (Osmani et al., EMBO Journal, 10:2669-2679 (1991); Osmani et al., Cell, 67:283-291 (1991)) may cause arrest or death in the fungi, improving the therapeutic outcome for patients with these infections.
The identification of effective small compounds which specifically inhibit signal transduction and cellular proliferation by modulating the activity of receptor and non-receptor tyrosine and serine/threonine kinases to regulate and modulate abnormal or inappropriate cell proliferation, differentiation, or metabolism is therefore desirable. In particular, the identification of methods and compounds that specifically inhibit the function of a tyrosine kinase which is essential for antiogenic processes or the formation of vascular hyperpermeability leading to edema, ascites, effusions, exudates, and macromolecular extravasation and matrix deposition as well as associated disorders would be beneficial.